The present invention relates to a method of fabricating a molded semiconductor device and a molded semiconductor device.
Heretofore, in the molding operation in the fabrication of a molded semiconductor device, in order to prevent the injected resin from leaking to the outside from between parts of outer leads, as shown in FIG. 1, there are provided tie bars 20 each of which couples adjacent leads 16 to each other, which are formed outside a molding line ML of a lead frame 11.
That is, in the molding operation, the resin which has been injected into a cavity between molding dies is prevented from leaking out across the tie bars 0 from between the parts of the outer leads by the function of the tie bars 20.
Then, in such a lead frame 11, in order to electrically isolate the leads 16 from one another after the completion of the molding operation, the tie bars 20 need to be cut away. The method of fabricating a semiconductor device employing a lead frame having the same tie bars as those in the above-mentioned case is, for example, disclosed in U.S. Pat. No. 3,762,039 (issued on Oct. 2, 1973). In particular, refer to FIGS. 2 and 6 and the description relating thereto in the U.S. Patent.
However, in the lead frame 11 in which the interval between the leads 16 is very small, as in the lead frame 11 which is used in LSI devices having multiple pins of a fine pitch (e.g., a pitch equal to or smaller than 0.3 mm), due to a limit in fabrication of the blade for cutting the tie bars 20, a limit in accuracy of the positioning between the cutting blade and the leads during the cutting of the tie bars 20, and the like, the cutting itself of the tie bars 20 become very difficult, so that in the first place, the provision of the tie bars 20 is not practical.
In addition, in the prior art lead frame 11 as shown in FIG. 1, since in the molding operation, the resin leaks out from the outer periphery of the package, it is necessary to remove the resin thus leaked out (i.e., fins of the resin) after the completion of the molding operation. However, in the case of the slenderer leads 16, the leads 16 may be readily deformed during the removal of the fins of the resin, and the resin fins which have been separated from the package and the leads may be caught between the shaping jig and the leads to degrade the lead shaping, and/or may be attached to other parts of the leads to cause bad lead contact during the mounting of the packages. Therefore, the removal of the unnecessary part of the resin requires a troublesome process which has to be effected carefully.
On the other hand, the lead frame may be provided with, instead of the tie bars 20, a tape which is stuck on the leads of the lead frame in a direction approximately perpendicular to the lengthwise direction of the leads. In such a lead frame, too, resin fins are unnecessarily produced, which will have to be removed by the above-mentioned troublesome process. A method of employing, instead of the tie bars, the tie tapes has, for example, been proposed in JP-U-62-114456 which was laid open on Jul. 21, 1987.